Investigation of Ti-substitution effects on structural and electrochemical properties of Na(0.)(67)Mn(0)(.)(5)Fe(0)(.)(5)O(2)batterycells

Ti-substituted Na(0.67)Mn(0.5)Fe(0.5)O(2)powders were fabricated by quenching at high temperatures, and the structural properties were investigated by Fourier transform infrared (FTIR), Scanning Electron Microscope (SEM), X-ray powder diffraction (XRD), and X-ray absorption spectroscopy (XAS) measurements. According to XRD analysis, it was not observed any impurity phases and it was found that the lattice constants of the powders were slightly increased by Ti content. The change in the valence state of both Mn and Fe ions was investigated by X-ray absorption near edge structure (XANES), and it was found that Ti-substitution caused a decrease in the valance state of Fe in Na0.67Mn0.5Fe0.5O2. Fourier transform (FT) of XANES showed that the local structure around the metal ions changed with the addition of Ti ions. The cycling voltammetry (CV) graphs of Ti-substituted cells were almost the same as the pure sample, which may not change the cycling mechanism in the cells. According to galvanostatic cycling measurements at room temperature, the best performance was obtained with Ti-substitution of 0.06 to 0.09 in the structure. The effect of environmental temperature in the battery cells was investigated at 10 degrees C to 50 degrees C, and it was found that the battery performance depends on the environmental temperatures.